The 78-year-old retired analyst for the Bureau of Labor Statistics views his Brightwood community as a waning example of a strong middle-class black neighborhood. He wants to draw attention to the plight of black residents in the District, even if it means chiding white residents who already have moved in.

“I don’t want people to come in and diminish the affordable housing stock for black Americans, because [black Americans] have nowhere else to go,” Ellis said. “There are plenty of places for white Americans to go.”

Ellis said he worries the District’s influx of younger, white residents could threaten black homeownership in the neighborhood, pushing even more black residents out of a place once widely known as “Chocolate City.”

Ellis’s fear is backed up by statistics showing the changing demographics of the District. In 1990, the city was 65 percent black. In 2010, according to the census, it was about 50 percent black.

In Ellis’s Northwest neighborhood, the black population has similarly declined, from 85 percent in 1990 to about 67 percent in 2010. This decline comes as the Hispanic population has jumped throughout the city and slightly more white residents have moved into Brightwood and other predominately black neighborhoods.

Brenda Parks, who oversees much of Brightwood for the Advisory Neighborhood Commission, said the Ward 4 neighborhood north of Petworth has seen positive changes in recent years. She pointed to increased home values, more safety and new businesses boosting the economy.

“There’s no such thing as too many white people living in the neighborhood. We need to get off this color thing,” said Parks, who is black.

“I don’t see it as a loss. I see it as a new chapter.”

Data from the Urban Institute shows that in Advisory Neighborhood Commission 4B — the local governing body that oversees nearly 20,000 residents in neighborhoods including Brightwood, Manor Park and Takoma — the median home price for the area in 2000 was $189,000. The real estate Web site Redfin now lists homes on the market in Brightwood for nearly $800,000.

About 70 percent of residents in that district owned their homes in 2012 — a rate that far exceeds the city’s average — and many, like Ellis and his neighbors, have lived there for decades. As residents leave or age out of their homes, Ellis says they’re not being replaced by other black families.

Ellis and his wife, Donna, who has been involved in the D.C. Democratic State Committee, are longtime activists in the city. Milfred Ellis, a graduate of the University of the District of Columbia, was involved in the local Civil Rights movement and participated in the 1963 March on Washington. The couple has hosted fundraisers at their home for Del. Eleanor Holmes Norton (D) and former Democratic mayors Adrian M. Fenty and Marion Barry. He printed his anti-gentrification signs on the back of old “I will boycott Walmart ” posters — posters he used to oppose Wal-Mart opening stores in the city.

Although gentrification is, by definition, wealthier residents displacing longtime poorer residents in neighborhoods, for Ellis, it’s about black residents not losing their foothold in the city. In the 1800s and 1900s, there was a sizeable black population in Georgetown, he noted, before it was transformed into the ritzy neighborhood it’s known as today.

Ellis said he hopes his signs — which have been visible for several weeks at his home on Peabody Street and haven’t attracted controversy in the neighborhood — will rally others in the community to fight for black homeowners. He hopes to launch a coalition that would fight for affordable housing in the city.

“I want to see a mobilization of African Americans come together and make changes and change the way we are thinking,” he said. “I don’t want to lead this fight, but I want to get it started. I want people to understand this. I want to educate the community.”

Not everyone seems on board with the effort.

Newly elected council member Brandon T. Todd (D-Ward 4) said he’s committed to “cultural diversity” in the ward.

Ellis’s 86-year-old next-door neighbor, who is black, raised her children in the Brightwood home, though none still live in the District.